A3000 Scan Doubler problem.

[shaf]

@x56h34

Hello, small world. I work at Victoria Park and McNichol just south of Steeles.

I would be interested to know if you have any local sources of Amiga stuff. I am tired of ordering from the U.S. and would prefer to buy locally.

Since Comspec changed to PC only I don't know of any other sources. Btwe if you ever had an Amiga repaired at Comspec between 1988 and 1993 I probably did it.

Cheers

Shaf

[x56h34]

Shaf,

The only source of Amiga hardware left in Canada are individuals like you and me. There is one active dealer that I know of, which is LiveWireSystems, however their stock is rather limited (only Amiga One and Elbox offerings...nothing like accelerators, or rare/fancy stuff).

BTW, are you still able to repair Amigas? Maybe you could fix this scan-doubler pot trouble for me? I have a friend who usually does these kind of repairs for me, but he's been rather busy lately and hard to get ahold of. I know how to solder and all, but only basic connections. I wouldn't dare touch a motherboard yet with my Walmart Soldering Iron (if you get my drift). :-)

[shaf]

x56h34

Yes I still do minor Amiga repair for the few people I know that still have Amigas, but due to time and resources I am not quick. (you try getting any work done with a 3 year old running around the house constantly wanting you attention!)

I have fairly good soldering skills but would prefer to wait a few week before attempting to take on the task. My only current Soldering Iron is a Weller 25 Watt. I am trying to replace my old 15 Watt unit that a friend borrowed and then broke.

Cheers

Shaf

[x56h34]

shaf,

This can certainly wait. I'm in no rush. Let me know when you are ready, if you're interested that is.

[voxel]

Hi :-)

Sounds like a cold solder join as the image comes up when you move the pot, have you looked at the pot solders ?

Many A3000 had that problem and making tree new good solders had cured it :-)

[voxel]

oups! double post!

[Noster]

Hi

> by Castellen on 2004/2/24 19:35:25

> You shouldn't really worry about using a non-metallic screwdriver as the brass
> screw of the pot should be electrically isolated from the circuit.
> There's no high frequency RF circuits in that region which will be effected
> by a metallic tuning tool either.

No, you should really use a non-metallic screwdriver (or one with a really small metal plate at the top), if I try to tune my flickerfixer of the A2000 with a normal metal screwdriver [Ok, I've not tested with the A3000T, but there is no need for tuning and I don't start testing it now :-)] I could bring the picture to stand, but in the moment I remove the screwdriver, the picture begins to run.
With the plastic screwdriver that is shipped with the A3000, it works.

So even if you have to resolder the pot, you should also use such a plastic screwdriver for tuning.

Noster

[x56h34]

@voxel:

Thanks for your suggestion. There's no doubt that this A3000's pot has bad solder connections underneath it, but I was thinking since I will be taking the whole unit apart maybe it would be smart to look for a better pot altogether. One with a knob which would stick out through the screw hole and be reachable outside of the case. Worst case scenario, I'll fix the solder connections and keep the original pot. :-)

[Castellen]

@ Noster:

Thanks for the info.
Haven't personally had that problem with any of the A3000s I've worked on.

As a radio communications engineer by trade, I usually have plenty of ceramic tuning tools about, but I have used metallic tools before on the A3000 and haven't noticed anything obvious.

Looks like the video circuit in that section is quite sensitive after all.  It's possible that the stray internal capacitance between the pot's isolated screw and the rest of the circuit is enough to cause problems in your case.


In which case a ceramic or plastic tool would be a far better option for other A3000 users as well.

[voxel]

@x56h34 :-)

quote:
to look for a better pot altogether. One with a knob which would stick out through the screw hole and be reachable outside of the case
endquote

I don't think you will find that kind of pot ;-) and even if you can I don't recommend such a modification.

As the circuit is made, you don't have to touch that pot more that one or two times in the whole life of your amiga.

And the pot used on the design is an endless multiturns model (so you can't break it by rotating it's knob too much, you will only ear a "clac clac" sound when you reach either sides and just turn the other direction to try to make a good tuning :-)

[x56h34]

Thanks Voxel! I will try and fix the solder joints and see what happens.